Various devices have been utilized as fluid dispensing apparatus, especially for fluids in liquid form, where the fluids are dispensed over an extended period of time at a predictable, substantially constant rate to the surrounding environment. One such device employs a gas-generating cell as a propulsion mechanism for the fluid.
One important aspect of such fluid delivery devices is shelf life of the device, particularly in high volume consumer applications, such as air freshener devices. In such applications, a shelf life of more than two years is typically required. Most known devices, however, are not designed for long shelf life, especially when they are mated to bladder-type fluid delivery reservoirs.
There are three major issues that affect shelf life of fluid delivery devices. First, shelf life is affected by the loss of moisture from the gas generating cell due to permeation through the gas chamber shell or through the flexible diaphragm. Since most of the reactions which generate hydrogen involve the consumption of water, desiccation of the cells typically will have a negative impact resulting in lower performance or shorter than desirable life. Second, if the gas generators are the type which consumes a metal, and oxygen is uncontrollably admitted to the cell, the metal will oxidize prematurely, and be spent when the device is to be activated. Third, if the gas generators are the type which consume a metal, hydrogen is generated to some degree prematurely. While corrosion inhibitors may be utilized to significantly reduce this effect, some hydrogen generation will occur if the active metal is in the presence of the aqueous solution, especially if the device is exposed to elevated temperature during storage. This hydrogen must be vented passively, otherwise the device will prematurely pressurize resulting in premature dispensing of the liquid, deformation of the device, or an undesirable burst of fluid delivery when the device is first activated.
Another concern exists with such fluid delivery devices that electrochemically consume a metal to form hydrogen in connection with the gas generator. With such devices, there is a delay before pumping of fluid occurs after the device is activated. This is caused by oxygen which has diffused into the headspace between the gas generating cell and the flexible diaphragm, which must be consumed before hydrogen generation begins.
There is yet another concern with such fluid delivery devices of the type which electrochemically consume a metal to form hydrogen. Typically, the metals utilized in such devices are amalgamated with mercury to reduce the amount of corrosion while being stored. This creates environmental concerns since mercury is toxic.
Among other things, the present invention is intended to address these as well as other shortcomings in the prior art and generally provides a device employing a gas-generating cell as a propulsion component to facilitate controlled release of a fluid to an ambient environment.